Gas compressor

ABSTRACT

A gas compressor of high wear-resistance comprising at least one set of a piston and a cylinder, preferably a ringless piston and a sleeveless cylinder, which are composed of an Al-Si alloy mainly containing eutectic crystals, preferably the piston being composed of a hyper eutectic crystals of an Al-Si alloy, the inside wall surface of the cylinder being formed of a chill structure layer.

United States Patent I19] Nishiyama et al. 1 Apr. 17, I973 GAS COMPRESSOR 3,306,738 2/!967 Young 75/148 3,033,626 5/1962 [75] Inventors: Keizo Nislliyama, Handa; l'likaru 2,096,092 10/1937 Takaoka; Sham Nakayarna, both of 3,610,110 10/1971 Kariya, all of Japan 73 Assignee: Kabushiki Kaisha Toyoda Jidoshok- 22:"

seisakusho Karlya'sh" Japan Attorney-Milton 1. Wayne et al. [22] Filed: Aug. 4, 1971 [57] ABSTRACT [21] Appl. No.: 168,982

A gas compressor of high wear-resistance comprising at least one set of a piston and a cylinder, preferably a [30] Foreign Application Priority Dam ringless piston and a sleeveless cylinder, which are composed of an Al-Si alloy mainly containing eutectic Aug. 8. 1970 Japan ..45/69387 crystals, preferably the piston being composed of a hyper eutectic crystals of an Al-Si alloy, the inside [52] 1.8. CI.... ..92/169, 75/[48 wall surface of the cylinder being formed of a Chill [51] Int. Cl ..F0lb 11/02 structure Myer. [58] Field of Search ..92/l69; 123/905]; 75/148 [56] References Cited 3 Claim, 6 Drawing Figures UNITED STATES PATENTS l0/l970 lzumi ..92/I69 PATENTED 7:973 3, 727, 524

SU RFACE F/ga PATENTEDAPR 1 T1915 5.727, 524

sum 3 or 4 PISTON CLEARANCE 0 2b 4b 6b 80 TEMPERATURE c) 0 2O 4O 6O 8O TEMPERATURE (C) PATENTEDAPR 1 11913 3'. 727. 524

sum u 0F 4 Fig. 6

oo -E 90- C 5 E 80- LL! 2 g 70- DJ 2 I) J O 0 16 2b 30 do PISTON CLEARANCE 1 GAS COMPRESSOR The present invention relates to a gas compressor provided with at least one set of a cylinder and a piston, and in particular to a gas compressor comprising at least one set of a sleeveless cylinder and a ringless piston which are both made of aluminum-alloy.

Generally, in the field of gas compressors, especially those mounted on vehicles for air-conditioning, there is an increasing use of aluminum alloys as cylinder material mainly for the purpose of making the weight thereof light. Usually a sleeve made of cast iron or ferrous sintered metal is fitted (by means of pressure insertion or integral casting) into the inside wall surface of the cylinder in order to prevent wear and sticking resulting from sliding friction between the piston and the aluminum alloy. Many studies on the adoption of aluminum alloys for use as piston material because of its lightness have been carried out in the various fields, and at the present stage it seems that hyper eutectic crystals of an Al-Si alloy with a silicon content of IS to 25 percent by weight brings about good results.

The hyper eutectic crystals of an Al-Si alloy are highly suitable in that in addition to its wear-resistance its thermal expansion coefficient is relatively small for an aluminum alloy and most closely approximates that of a sleeve made of iron base alloys. However because its thermal expansion coefficient is not exactly equal to that of the iron base alloys it is very difficultto maintain the clearance between the piston and the inside wall surface of the cylinder (referred to as piston clearance hereinafter) constant during operation. That is, if the piston clearance is set to be correct at a high temperature, the clearance at a low temperature whereat it is particularly required to utilize the compressor capability is large owing to the thermal expansion difference between the piston and the cylinder and thus the volumetric efficiency of the compressor is reduced. While if the choice is made so as to be correct at a low temperature the clearance at a high temperature is extremely small, which leads to sticking which is one of the main drawbacks preventing the speeding up of the compressor.

It is, therefore, an object of the present invention to eliminate the aforementioned disadvantages.

It is another object of the present invention to provide a novel compressor of highwear-resistance in which a piston and a cylinder are both composed of an Al-Si alloy.

It is still another object of the present invention to provide a novel compressor in which a ringless piston and a sleeveless cylinder are used.

As a result of various studies on the sleeveless cylinder with the object of producing a compressor which is light in weight and capable of being speeded up and also easy to make, the applicants have found that a combination of a piston and cylinder having approximately the same wear-resistance as that of the conventional compressor using a sintered sleeve may be obtained by using hyper-eutectic crystals of an Al-Si alloy as the piston material and forming in the inside wall surface of the eutectic crystals an Al-Si alloy cylinder, a compact chill structure of high wear-resistance provided through the use of die casting.

In general, it is well-known that when an Al-Si alloy is subjected to improved treatment or quenching a eutectic crystal structure comprising fine particles uniformly distributed therein may be obtained. This crystal structure is difficult to deform under the action of external force and otherwise excellent in mechanical qualities. It is thought that this may be attributed to the fact that by refining and granulating silicon crystals the degree of stress concentration surrounding the silicon crystals is allowed to distribute be distributed and thus reduced whereby the stress distribution in the material is made uniform. This effect is also beneficial for wearresistance.

In general, it may be estimated from the uniformity of carbide through the spheroidization of alloy steel and chill structure of white metal. etc. that ifa soft substrate is under-laid by a harder phase, the finer and more uniform is the distribution of the phase. In other words, the finer the hard particles, and the shorter the distance between the adjacent particles, the better the resulting properties such as wear-resistance.

The present invention is substantially based on the above-mentioned theory and it has therefore become possible to provide a novel gas compressor comprising at least one set of a piston and a cylinder, both composed of an Al-Si alloy mainly containing eutectic crystals, the inside wall surface portion of said cylinder being formed ofa compact chill structure layer.

In the preferred compressor according to the present invention the cylinders of an may be made of eutectic crystal Al-Si alloy and the piston may be made of hyper eutectic crystals of an Al-Si alloy.

Further, because the present invention provides a ringless piston and a sleeveless cylinder, the design of the compressor is much simplified.

The advantages and other objectives according to the present invention will be better understood from the following examples with reference to the accompanying drawings wherein,

FlG. l is a cross-sectional side view of one of the preferred compressors according to the present invention,

FIG. 2 is a microscopic photograph showing the surface structure of the cylinder cut along the [1-H line in FIG. 1,

HO. 3 is a microscopic photograph showing the deeper structure of the cylinder cut along the Ill-[ll line in FIG. 1,

FIG. 4 is a characteristic diagram showing the relation between temperature change and piston clearance,

FIG. 5 is a characteristic diagram showing the relation between temperature change and thermal expansion for various materials, and

FIG. 6 is a characteristic diagram showing the relation between piston clearance and volumetric efficiency.

Referring to FIG. I, l is a cylinder, 2 a ringless piston, 3 crankshaft, 4 the portion accommodating the ringless piston, 5 valveplate, 6 suction chamber, and 7 exhaust chamber.

Cylinder I may be produced by die casting using an aluminum-silicon mixture in which the silicon content is such that normal eutectic crystals or eutectic crystals having a small amount of hyper-eutectic crystals may be formed. Through the die casting operation, the surface of the cylinder is quenched to provide a chill structure. As is apparent from FIG. 2, the chill structure appearing on the inside wall surface portion is composed of eutectic crystals including a small amount of primary crystals (dendrite) incorporated into fine silicon crystals. In this case, the chill layer is supercooled by quenching and the eutectic point of the Al-Si phase diagram deviates in the right hand direction and thus a small amount of hyper-eutectic crystal composition may be converted into eutectic crystal structure without depositing primary crystals of silicon. However, the portion deeper than the chill layer is supercooled to a less extent as the cooling rate therein is relatively slow. Therefore, the wear-resistant primary crystal of silicon deposits, but the coarse needle-like silicon eutectic crystals develops throughout as shown in FIG. 3 which leads to reduction in wear-resistance. It is known from the preceding report that the wear-resistance of an Al-Si alloy increases as the silicon content approaches the eutectic crystal composition, but if the silicon content exceeds the eutectic crystal composition, the wear-resistance does not further increase, which fact is attributed to the presence of the primary crystals of silicon. In this connection, it is natural that the strength deteriorates as the primary crystals of silicon deposit out. Accordingly. it will be understood that the silicon content must be limited when the compressor is operated under a high pressure as in the present invention.

In accordance with the present invention a compact chill structure layer to be formed and retained in the inside wall surface portion of the cylinder may be produced by using a die-casting.

In this manner, there is present a compact chill structure layer in the inside portion adjacent to the surface layer which prevents blow hole defects such as fine pinholes, which tend to develop in the inside from emerging to the surface, so that it plays an effective part in maintaining an air-tight surface like a moulding surface. And simultaneously, by the positive use of this chill structure layer, an effective, practical wall surface of the cylinder may be obtained without any particular surface treatment.

The following table shows the comparison of wear of the present compressor with the conventional compressor in which hyper-eutectic crystals of an Al-Si alloy are used in the piston and a ferrous sintered metal sleeve is used in the cylinder. The table was compiled from a continuous test over 500 hours carried out under the conditions of 4600 rpm, 22 to 24 kg/cm' maximum cylinder pressure, and an intermittent test over 400 hours carried out under the conditions of 4800 rpm, 19 to kg/cm maximum cylinder pressure, and operating times of sec on and 5 sec off.

TABLE (milimmus lllll'l'lllillt'lll (ultliuunus (I l l ti I) 5 l lll ll 3 lislnn t limlvr l'istmx (Tylimlm The combination of a cylinder and piston, in accordance with the present invention, is characterized in that the relative thermal expansions function to extend slightly the piston clearance at a high temperature rather than that at a low temperature. As can be seen from FIG. 4 and FIG. 5 with the conventional compressor the thermal expansion coefficient of the sleeve made of ferrous sintered metal is less than that of the piston composed of hyper-eutectic crystals of an Al-Si alloy, so that the piston clearance progressively diminishes with increase oftemperature.

In FIG. 4, curve A is for the present compressor, comprising the eutectic crystals Al-Si and hyper eutectic crystals of an Al-Si alloy system, and curve B for the conventional compressor comprising an Fe and hyper eutectic crystals of an Al-Si system. In FIG. 5, curve C indicates eutectic crystals of an Al-Si alloy, curve D hyper eutectic crystals of an Al-Si alloy and curve B ferrous sintered metal, respectively.

Now, if an appropriate clearance (about 10 p.) is required in the neighborhood of the highest temperature (about 100C) the clearance at a low temperature becomes extremely large (about 34 p) which reduces the volumetric efficiency. In contrast, with the compressor in accordance with the present invention an appropriate clearance (about l0 t) set at a low temperature increases only to 25 ,u. in the neighborhood of the highest temperature as the thermal expansion coefficient of the cylinder is rather larger than that of the piston. However, a high volumetric efficiency is required when the temperature is low i.e. when the cooling effect is insufficient rather than when the temperature is high i.e. when the cooling effect is excessive and therefore it is important to maintain the appropriate piston clearance at a low temperature as in the present invention.

FIG. 6 is a characteristic diagram showing the relation between the piston clearance and the volumetric efficiency and it may be suggested from this diagram that the piston clearance preferably falls within the range of about 10 to 30 11..

As stated above, the compressor according to the present invention is constructed in such a manner that the ringless piston composed of hyper-eutectic crystals of an Al-Si alloy moves within the sleeveless cylinder composed of an Al-Si alloy having eutectic crystal structure. In this construction it is possible not only to omit the cylinder sleeve and piston ring of the prior art and to eliminate the time required for fitting these members to the cylinder or piston. but also to set the piston clearance under a low temperature condition without taking any precaution to meet the situation at a 'Ilw prior mmprvssur lllll'lllllllllll It will be apparent from the results that the present high temperature, whereby the improvement in volucompressor is entirely free from sticking and superior metric ff i d h d bili f h commasto the conventional compressor concerning wear-resistance.

sor for speeding up is obtained.

Furthermore, the compressor according to the 6 present invention has the advantage that as the inter piston and a cylinder accommodating said piston face friction between aluminum alloys is smaller than wherein that between aluminum alloy and ferrous sintered said piston is composed ofa hyper-eutectic crystalmetals and the vibration absorption factor of aluminum v alloy;

alloy is larger than that of ferrous sintered metals it i 5 said cylinder is composed andALSi alloy mainly possible to remarkably reduce noise during operation. c( )mf1mmg eutect'c crystal Th invention h been described in detail with pap the inside wall surface of said cylinder 18 formed of a ticular reference to a preferred embodiment thereof, chinstrucmre layer but it will be understood that variations and modifica- A gas compressor according m clmm wherem tions can be effected within the spirit and scope of the said cylinder is a sleeveless cylinder.

invention as already described above- 3. A gas compressor according to claim I, wherein What we claim is:

said piston is a ringless piston. l. A gas compressor comprising at least one set of a 

1. A gas compressor comprising at least one set of a piston and a cylinder accommodating said piston wherein said piston is composed of a hyper-eutectic crystalline Al-Si alloy; said cylinder is composed of an Al-Si alloy mainly containing eutectic crystals; and the inside wall surface of said cylinder is formed of a chill structure layer.
 2. A gas compressor according to claim 1, wherein said cylinder is a sleeveless cylinder.
 3. A gas compressor according to claim 1, wherein said piston is a ringless piston. 